A novel configuration for a Brillouin distributed sensor using a phase modulated probe is presented. It offers the combined advantages of a direct implementation using simple devices and a large immunity to noise, shifting the information from the baseband to a higher frequency, which substantially strengthens the robustness to perturbations, interferences and other optical coherent noises. It naturally facilitates the possibility to perform frequency-coding on the probe to realise dynamic and fast measurements, since all frequency tunings are realised at sub-GHz frequencies.